GSSAP, also known as GEO-SSAP, is a USAF (U.S. Air Force) mission with the objective to provide significant improvement in space object surveillance, not only for better collision avoidance, but also for detecting threats. The previously classified program was declassified during a speech in March 2014 by General William Shelton, commander of the US Air Force Space Command. 1)

In February 2014, the USAF (United States Air Force) lifted the veil of secrecy on its previously classified GSSAP which will operate in conjunction with ground-based radars and telescopes to observe potential threats from foreign space objects. Currently, the Air Force tracks some 23,000 pieces of orbiting debris larger than ~10 cm at distances of up to~ 37,000 km above Earth's surface. 2)3)

The GSSAP satellites will be a spaceborne capability operating in the near-geosynchronous orbit regime supporting U.S. Strategic Command space surveillance operations as a dedicated SSN (Space Surveillance Network) sensor. The GSSAP satellites will support JFCC SPACE (Joint Functional Component Command for Space) tasking to collect space situational awareness data allowing for more accurate tracking and characterization of man-made orbiting objects. It will have a clear, unobstructed and distinct vantage point for viewing resident space objects orbiting earth in a near-geosynchronous orbit without the disruption of weather or atmosphere that can limit ground-based systems. Data from GSSAP will uniquely contribute to timely and accurate orbital predictions, enhancing our knowledge of the geosynchronous orbit environment, and further enabling space flight safety to include satellite collision avoidance. 4)

The GSSAP constellation will consist of four satellites, launched in pairs from Cape Canaveral, FL AFS (Air Force Station).

Spacecraft:

The two GSSAP spacecraft were built by Orbital ATK of Dulles, VA, as prime contractor. Exact details on the satellites and their payloads have not been provided.

With a mass estimated on the order of 650 to 700kg, each GSSAP satellite likely carries a significant amount of propellant, most likely using a hydrazine monopropellant propulsion system to make frequent orbit adjustments and perform stationkeeping maneuvers when operational requirements call for the satellite to drift to or stay at a new location. Small impulse burns will set the satellite up to observe chosen targets by setting up favorable passes below or above the satellite of interest at a low relative speed. 5)

Power generation is accomplished using two deployable solar arrays while a high-rate communications system provides the secure downlink of acquired SSA sensor data.

It can be expected that one GSSAP satellite operates in a drift orbit above GEO while the other orbits below the GEO altitude.

Launch: The second pair of GSSAP-3 and GSSAP-4 satellites were launched on August 19, 2016 (04:52 GMT) on a Delta-4M+(4,2) vehicle of ULA (United Launch Alliance) from Cape Canaveral (SLC-37B), FL. 9)

Payload:

Imager: The satellites carry an electrooptical sensor to be able to characterize the satellites in GEO (Geostationary Orbit) by tracking their activity, keeping tabs on satellites that are frequently maneuvered. It is likely that the satellites are conceptualized to carry radio sensors to track radio emissions from satellites as an indicator of satellite identity and activity.

ANGELS (Automated Navigation and Guidance Experiment for Local Space)

A hosted payload on this flight is ANGELS, two small satellites of AFRL (Air Force Research Laboratory). The objective of ANGELS is to test accelerometers and specialized algorithms that will utilize the GPS navigation signals for precision guidance when in close proximity to other satellites, thereby reducing the probability of a collision.

ANGELS will evaluate SSA techniques in a limited region around its Delta-4 launch vehicle upper stage several hundred kilometers above GEO, testing maneuvering concepts around the rocket body. The vehicle will begin experiments approximately 50 km away from the upper stage and cautiously progress over several months to tests within several kilometers. As part of the research effort, ANGELS will explore increased levels of automation in mission planning and execution to enable more timely, safe, and complex operations with a reduced operations footprint. AFRL engineers will maintain positive control of the spacecraft throughout the automation experiments with ground commanded authorization to proceed points, ensuring a "man-in-the-loop" throughout the experiment. The Air Force will use the results to evolve the ability of future systems to responsively perform SSA from a modest but safe distance. 10)

Status of mission:

• Sept. 14, 2017: The 1st Space Operations Squadron at Schriever Air Force Base, Colorado, accepted two new satellites into operation Sept. 12 to expand their Geosynchronous Space Situational Awareness Program's ability to characterize and track objects in space to support a neighborhood watch out in orbit. 11)

- GSSAP became operational in September 2015, when the first two GSSAP satellites reached their Initial Operational Capability. The two newest satellites to the program, GSSAP 3 and 4, were launched into orbit Aug. 19, 2016, and have now finished their testing phase.

- "GSSAP -3 and -4 will significantly enhance our ability to characterize objects on geosynchronous orbit," said General Jay Raymond, commander of Air Force Space Command. "This provides the awareness we need to successfully operate in space."

- This addition to GSSAP is vital to expand 1st SOPS (Space Operations Squadron)'s space-based space situational awareness mission. It not only provides a significant improvement in space object characterization, but also in detecting threats. Because of its near-geosynchronous orbit, it has a clear and distinct vantage point to avoid the weather interruptions that can limit ground-based space surveillance systems.

- The GSSAP constellation can characterize objects in space to a very refined level. Being able to discriminate and characterize objects assists the U.S. and its allies in achieving responsible and safe use of space. The information obtained by this program provides robust spaceflight safety information and ensures free access to, and use of, space.

• In 2017, Orbital ATK started work on two more surveillance satellites for the U.S. Air Force's geosynchronous neighborhood watch program late last year as the military aims to expand its ability to track and investigate other objects in the heavily-trafficked belt at 35786 km over the equator. Orbital ATK disclosed it started working on the GSSAP-5 and -6 satellites. 12)

- The declaration of IOC for GSSAP concludes successful testing of the system and brings on line an SSA (Space Situational Awareness) capability that will improve the ability to rapidly detect, warn, characterize and attribute disturbances to space systems in the geosynchronous (GEO) environment. The system reduces the likelihood of space collision, increases safety in this domain and will support USSTRATCOM's Unified Command Plan-assigned mission to plan and conduct SSA.

- GSSAP's maneuverability and vantage point near GEO make it a valuable addition to existing U.S. operational assets. Other assets conducting SSA of GEO, which GSSAP complements, include the SBSS (Space Based Space Surveillance) system, which operates in LEO, and multiple ground-based sensors.

- The SMC (Space and Missile Systems Center), located at Los Angeles Air Force Base, operated the satellites during nearly a year of developmental testing. At the conclusion of testing, the Space and Missile Systems Center turned operational control of the satellites over to 14th Air Force, which was delegated to the 1st Space Operations Squadron, 50th SW, for operational test and evaluation.

• Jan. 12, 2015: The two GSSAP satellites are capable of approaching and observing nearly 600 satellites in geosynchronous orbit, two former chief scientists for Air Force Space Command wrote in the November-December 2014 issue of the Air & Space Power Journal, a professional journal published by the Air Force Research Institute. 15)

The information compiled and edited in this article was provided byHerbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).